|Burned out Arduino Mega 2560 5v regulator- upper left next to the power plug. Note the big hole blown in it!|
I tried searching the forums and general google searching to try and find the root cause. No luck- and forum responses were generally about making sure the power supply polarity was correct, etc. After finishing the searches and looking through reprap.org's RAMPS 1.4 page, I thought a possible cause might be some mismatch between the 12v power supply and the power supplied by the USB cable from the PC. The D1 diode on the RAMPS board allows the 12v power supply to also supply power to the Arduino. If the D1 is cut, the Arduino must be powered off the USB- but it wouldn't receive any potentially troublesome power from the RAMPS board. So, I decided to cut the D1 diode. Worst case I can solder in a new diode.
It was pretty tough to actually cut the D1- it's tucked way down next to the stepper driver sockets. (under the "x" and "y" stepper drivers) I ended up cutting it using the tip of an x-acto knife.
|D1 is the small black / silver cylinder in the center left of the frame|